1. Field
This application generally relates to the launch of flight vehicles, specifically to enabling the launch of ballistic rockets and aero-assisted flight vehicles (spaceplanes) from conventional runways, without use of, respectively, dedicated ground launch structures or dedicated runways.
2. Prior Art
From the dawn of Space Era through present time, all space launches—sub-orbital, orbital, and beyond—have been accomplished almost solely using ballistic (wingless) rockets launched from the ground. This approach requires dedicated ground launch structures for assembling and servicing the rockets before launch. Also, the launch structure must hold the rocket in a vertical position until lift-off and must deflect the exhaust plume in a safe direction to prevent erosion of the ground and structure under the launch pad. These launch structures are expensive to build and expensive to operate. There are a limited number of them around the world, which places substantial operational limitations on access to space.
An alternative to a vertically launched ballistic rocket is an aero-assisted “winged” spacecraft, or a spaceplane—a vehicle which can take off horizontally from a runway like a conventional airplane. Such a spaceplane is known as an aero-assisted vehicle because it uses wings and their interaction with the air to provide lift. In order to minimize aerodynamic losses during ascent through the atmosphere, the spaceplane must have high wing loading; i.e., the ratio of the spaceplane's weight to its wing area must be relatively large. As a result, such high wing loading entails extremely high take-off airspeed, which is incompatible with the use of the runways of most conventional airfields.
The use of a non-powered glider to launch an aero-assisted spacecraft or spaceplane from a conventional runway is discussed in U.S. Pat. No. 5,255,873 to R. Nelson (1993). Nelson proposed a non-powered reusable wing glider attached to the upper surface of the spaceplane to form a glider-spaceplane “stack”. Nelson envisioned a prolonged subsonic flight of the stack through a substantial part of the lower, dense atmosphere, with staging (separation of the wing glider from the spaceplane) occurring at an altitude of about 5 km. Thus, the wing area of the glider is substantially constrained in order to reduce atmospheric drag, resulting in a very high take-off airspeed of over 500 km/h (280 knots). This requirement for very high take-off airspeed is unrealistic since it greatly exceeds existing technical capabilities of conventional technologies used for the undercarriage of existing flight vehicles, it also severely limits the choice of acceptable runways that can accommodate such operation.
In addition, Nelson's glider had no undercarriage and was dependent upon the spaceplane to provide an undercarriage, thus limiting payload diversity. The undercarriage was subsequently dropped from the spaceplane after take-off Also, the wing planform (i.e., the contour of the wing as viewed from above) of the glider was constrained to a specific shape configured with a high aspect ratio. This limitation resulted in weaker mechanical strength as compared, for example, with a delta wing, which has an aspect ratio close to unity. In addition to the above, Nelson's glider could not be used as a launch platform for ballistic rockets. To best of my knowledge, this concept was never used for launch to space.
Another alternative to the launch of ballistic rockets from the ground is an air-deployed, lift-assisted launch. The vehicle to be launched is carried to the desired launch point by a customized airplane. At the launch point, the vehicle is released from the airplane, and the propulsion system of the vehicle is activated. This method of launch has been known for a few decades. A detailed review of various versions of this approach is published by N. & M. Sarigul-Klijn (AIAA Paper 2001-4619). The only successful implementation of this approach for actual launches to space that I am aware of is the launch of a ballistic rocket suspended under a conventional aircraft, as shown in U.S. Pat. No. 4,901,949 to A. Elias (1990). In this method, the rocket is partially aero-assisted. It has a small wing to facilitate initial ascent of the vehicle.
As for the launch of aero-assisted vehicles, the only approaches I have found are shown in U.S. Pat. Nos. 5,626,310 and 6,029,928 to M. Kelly (1997, 2000). Kelly envisioned towing the aero-assisted launch vehicle as a glider by a conventional aircraft. Due to high wing loading of the vehicle, the towing plane must take off while the towed vehicle to be launched is still rolling out. Thus a relatively long runway is required. Insofar as I am aware, this method has never been used in practice.
Lift-assisted, air-deployed launch of spaceplanes is also known. The research rocket plane X-15, made by North American Rockwell, was the first spaceplane in early 60s of the last century that actually reached space beyond altitude of 100 km. More recently, a private spaceplane named SpaceShipOne, made by Scaled Composites, made three successful flights to space to even higher altitudes. X-15 was launched from a customized B-52 bomber, and SpaceShipOne was launched from a custom-made high-altitude jet plane named White Knight.
In all known air-launch methods, the vehicle is delivered to the desired launch altitude high in the atmosphere by the carrier aircraft as a passive payload. This places a substantial limitation on the initial weight of the launch vehicle. Not incidentally, Orbital Sciences Corp., the assignee of the Elias patent, is currently using this method for launches of their smallest rocket, Pegasus, while larger rockets produced by this company are launched from conventional ground facilities.
To sum, ground launch to space is associated with need to use expensive ground structures for rockets and/or dedicated runways for spaceplanes. The air-launch to space is associated with limitations on initial weight for space launch vehicles, both rockets and spaceplanes. Thus all launches of rockets and spaceplanes to space have heretofore substantial operational limitations.
My patent (U.S. Pat. No. 8,168,929) shows a non-powered pre-stage with a commensurably large wing area for launching a variety of single-stage and multiple-stage space vehicles, (e.g., conventional ballistic rockets and prospective spaceplanes) from conventional runways. This method of launch eliminates need for dedicated ground launch structures and/or dedicated long runways. The vehicle to be launched is mated to a non-powered aero-assisted pre-stage (NAP), with their flight directions aligned, using a lock-and-release mechanism. The resulting stack takes off like a conventional airplane using the propulsion of the vehicle and aerodynamic lift of the NAP. After the desired trajectory of the vehicle is achieved, the vehicle is separated from the NAP and continues its ascent. The NAP returns to the surface for reuse or disposal. Thus, a wide variety of conventional airfields can be used for launch of ballistic and aero-assisted flight vehicles. The key benefit of the NAP is the capability to enable the launch of ballistic rockets and aero-assisted flight vehicles from conventional runways. However, early use of the propulsion system of the vehicle to be launched, before the vehicle reaches the desired ascent trajectory, may lead to additional expenditures of propellant, which in turn could result in payload mass penalties.